Counter current crystallizer

ABSTRACT

Improved apparatus for operating a continuous process for the freeze concentration of aqueous solutions, such as fruit juices, wine, beer, coffee extract and the like.

This invention relates to an improved apparatus for operating acontinuous process for the freeze concentration of aqueous solutions,such as fruit juices, wine, beer, coffee extract and the like. The kindof processes with which the apparatus is concerned comprises passing theaqueous solution through a succession of disperate cooling zones,separating the ice crystals of each cooling zone from the liquid of thatzone and passing these crystals to the preceding cooling zone, whilerecovering the liquid of the last cooling zone and feeding out the icecrystals of the first cooling zone.

A process and apparatus of this kind has been described in U.S. Pat. No.3,283,522 (Ganiaris).

One object of the invention is to provide an apparatus, which is moreeconomic, especially in scaling up, and which is easier to operate.

Another object of the invention in specific preferred embodiments is toavoid liquid vapour interfaces in operating the apparatus in order toavoid loss of volatile aroma constituents and contact with air.

Still another object of the invention in specific preferred embodimentsis to minimize the quantity of wash water needed.

According to the invention there is provided an apparatus for thecontinuous freeze concentration of aqueous solutions comprising incombination:

(a) enclosure means defining a cylindrical crystallization zone;

(b) a rotatable axle coaxial with the crystallization zone mentionedunder (a);

(c) a plurality of cooling trays within the crystallization zonementioned under (a), distributed at preselected distances along the axlementioned under (b), and substantially perpendicular to that axle, saidcooling trays extending in radial direction from the inner wall of theenclosure means mentioned under (a) to the axle, such as to divide thecrystallization zone, mentioned under (a) in a number of coolingcompartments;

(d) wiper means, adapted to cooperate with and wipe the surface of thecooling trays, mentioned under (c);

(e) means to separate the ice crystals of each of the coolingcompartments, mentioned under (c) from liquid in that compartment;

(f) means belonging to each cooling compartment to separate the icecrystals of the second and additional cooling compartments from liquidand pass said ice crystals to the preceding compartment;

(g) means to pass liquid obtained from the second to the penultimumseparating means mentioned under (f) to the succeeding coolingcompartment;

(h) means to separate the ice crystals of the first cooling compartmentfrom the liquid and feed out said ice crystals;

(i) means to pass liquid obtained from the first separating meansmentioned under (h) to the second cooling compartment;

(j) means to feed in the aqueous solution in the first coolingcompartment;

(k) means to recover liquid obtained from the last separating means as aproduct.

When speaking of preceding and succeeding these terms are meant to referto the cooling compartments in the sequence of concentration ofdissolved solids in the liquid.

When speaking above of "cooling trays" a convenient embodiment will beflat plates, being hollow such as to contain and conduct a coolingmedium, such as evaporating fluorinated hydrocarbons (freon).

The "wiper means" mentioned above will generally be scrapers, adapted toactually scrape the surface of the cooling trays; but wiper means atvery close distance skirting along the surface of the cooling meanswithout actually touching are not excluded.

The means mentioned above under (h) will preferably comprise a washcolumn, and the means mentioned under (f) will preferable compriseslurry thickeners. Conveniently the wash column and the slurrythickeners will be of a novel design according to the invention, theconstruction of both being based on the principle which now will bediscussed.

According to this aspect of the invention there is provided an apparatusfor the continuous thickening and as the case may be washing of an iceslurry, said apparatus being usable as the means mentioned above under(f) and (h), comprising in combination the following cooperatingelements.

(a') enclosure means defining a cylindrical space;

(b') a rotatable axle coaxial with the enclosure means mentioned undera', said axle and said enclosure means defining together an annularcylindrical space;

(c') means to feed in the feed slurry to the space mentioned under (b');

(d') filter means in said space, adapted to drain fluid from the slurrywhilst retaining ice crystals, present in that slurry;

(e') means, adapted to feed out the thickened slurry;

(f') means adapted to feed out the fluid drained out by the filter meansmentioned under (c');

(g') means adapted to maintain a pressure difference between the feed inslurry and the drained out fluid such as to ensure a stream of fluidthrough the filter means;

(h') between the means mentioned under (c') and (e') mechanical meansadapted to push a mass of ice crystals to the feed out for the thickenedslurry mentioned under (e').

Normally the slurry thickener will also comprise separately or incombination:

(i') mechanical means between the filter means mentioned under (d') andthe feed out means mentioned under (e') having the following functions

providing a limited resistance to the passage of a mass of ice crystalsand cooperating with the mechanical means mentioned under (h') in such away as to compact the mass of ice crystals squeezing out liquid frombetween the separate ice crystals;

desintegrating the compacted mass of ice crystals such as to facilitatethe passage of the particles obtained;

(j') vanes attached to the inside of the cylindrical enclosure means,mentioned under (a') adapted to avoid that the compacted means of icecrystals rotates along with the rotatable axle, the mechanical meansmentioned under (h') or the mechanical means mentioned under (i').

The mechanical means mentioned under (h') may e.g. comprise tilted vanesdistributed along the circumference and attached to the rotatable axlementioned under (b'). Tilted vanes, as the case may be provided with asharp edge, may also be used to desintegrate the compacted mass of icecrystals as mentioned under (i'). Preferably however, the meansmentioned under (i') will comprise a rotating disk with knives and slotsas will be more fully disclosed below.

In order to help in the creation of a packed bed of crystals in theannular space it may be necessary to employ special means to avoid themass to rotate along with the mechanical means, such as the tiltedvanes, rotating with the rotatable axle. These means may consist ofvanes attached to the inside of the cylindrical enclosure means,oriented radially and parallel to the axis of the enclosure means andpreferably located at both sides of that part of the annular space whichcontains the filter means mentioned under (d'). According to a preferredembodiment of the invention the filter means mentioned under d'constitutes part of the enclosure means mentioned under (a'), which goesto say that the cylindrical wall is for a certain length perforated allaround such as to constitute a filter adapted to drain away fluid in theslurry and retain the ice crystals. Preferably the dimensions of theapparatus have to be chosen such that the length of the packed bed,created in the annular space, mentioned under (b') is several times itswidth preferably between 7 and 15 times.

According to another embodiment of the invention the filter meansmentioned under (d') consists of radially oriented pairs of filtersurfaces, bridging the annular space, mentioned under (a'), the twofilter surfaces of each pair being held apart by spacing means such asto create a narrow passageway for drained out fluid, that passagewaybeing connected to the feed out means for the drained out fluidmentioned under (f').

The present invention will now be further described with reference tothe accompanying drawings, in which:

FIG. 1 is a schematical representation of the total set-up showing anembodiment in which at the left a stack of crystallizing compartments isshown, at the right a stack of slurry-thickeners, one being modified toserve as a wash column

FIG. 2 is a compartimentalized crystallization vessel cut openlengthwise, in more detail

FIG. 3 is a cross-section along the line III--III in FIG. 2

FIG. 4 is a cross-section along the line IV--IV in FIG. 3

FIG. 4A is a preferred embodiment of the apparatus of the invention,partly cut open lengthwise, in which each slurry thickener is separatilyattached to a crystallization compartment and has its own drive and aseparate wash column is attached to the apparatus

FIG. 5 is a slurry thickener cut open lengthwise as corresponds with(19) in FIG. 1

FIG. 6 is a cross-section according the line VI--VI of FIG. 5

FIGS. 6A, 6B and 6C are representations of a preferred embodiment of aslurry thickener

FIG. 7 is a cross-section clarifying another embodiment of the means forseparating crystals and liquid to be used in a slurry thickener-washer.

FIGS. 8, 8A and 8B show the wash-column of FIG. 4A in more detail.

An example of the apparatus according to an embodiment of the inventionand the manner it operates will now be described. We refer to FIG. 1,which is a schematical representation of the total set-up.

At (1) a reservoir is shown containing the, as the case may bepre-chilled, liquid (such as fruit juice, coffee extract, wine and thelike) to be freeze concentrated. The liquid is pumped by pump (2),shunted by the pressure valve (3), set to maintain a predeterminedpressure in the first compartment of the crystallization vessel (4),provided with the axle (5), rotatable by the motor (6). The vessel (4)is divided into five compartments (7), (8), (9), (10), (11), by thecooling trays (12), (13), (14), (15), which are mounted on thecylindrical wall of the crystallization vessel (4) (in- and outlets ofthe cooling medium are indicated with arrows). Leakage from onecompartment to the other along the slits between the rotating axle andthe cooling trays may be prevented by conventional elastomeric rings(not shown).

For the sake of simplicity in this figure only two of the scraping means(16) and (17) are shown, which are attached to the axle (5). Asuspension of ice crystals is sucked out of compartment (11) to the feedin (18) of the thickener (19) by the pump (20). At (21) tilted vanes,attached to the rotatable axle (22), actuated by the notor (23) areshown. In the annular space (24) a packed bed of thickened slurry iscreated. (It has to be remarked that preferably this annular space isnarrower than is shown in the figure!) Liquid is drained away throughthe filter (25) by action of the pump (20). The packed bed is pushedupward and is finally desintegrated by the sharp edged tilted vanes(26). The broken up mass is flushed away by the liquid sucked away fromthe compartment (10) by the pump (27) through the filter (28) of theslurry thickener (29). The mixture of ice crystals from compartment (11)and liquid from compartment (10) is fed in compartment (10) at (46).

Liquid of compartment (11) is ultimately fed out at (30) through valve(31) to reservoir (32).

The valve (31) is actuated by the mechanism (31') which is controlled bythe sensing device (33), sensing the temperature of this pumped liquidand thus also the temperature in compartment (11).

In the slurry thickener (19) the stationary vanes (35) and (36) areshown which, as mentioned above, help in creating a packed bed in theannular space.

Rotating pens (47) are shown which help to keep the crystals insuspension. Stationary pens (48) are attached to the inside of thecylinder.

The slurry thickeners (19), (29), (34) and (37) operate essentially inthe same way. They and the thickener (38) which acts actually as a washcolumn are stacked together as shown and need only one axle (22). Inthis wash column (38) the ice has to be washed by water. As of course,dilution of the liquid in compartment (7) has to be avoided as much aspossible the quantity of wash water has to be kept as small as possible.Hence, water may not penetrate to the filter (39). This also avoidswater freezing on that filter, which would cause clogging.

The compacted mass of ice crystals after being broken up by the tiltedvanes (40) is flushed away by water pumped by the pump (41) and partlyor completely melted by passage through the melter (42). The quantity ofwater drained away is controlled by the valve (43), which is actuated bythe mechanisms (44), acting on the sensing device (45). By measuringe.g. the temperature this device detects the concentration of the liquidsurrounding the ice crystal at the point where it is located and keepsit substantially constant by controlling the valve (43). When theconcentration, as indicated by the temperature of the liquid surroundingthe ice crystals, is below a preselected value the valve (43) opens,when the concentration of the liquid surrounding the ice crystals isabove a preselected value valve (43) closes.

The compartimentalized crystallization vessel, denoted with (4) in FIG.1 is shown in more detail in FIG. 2, cut open lengthwise.

At (101) we see the cylindrical vessel, divided in compartments (102)etc., separated by cooling trays (103) etc. The cooling trays are wipedby scrapers (104) etc., provided with the plastic flaps (105) etc. Thescrapers are attached to the axle (106), actuated by the electric motor(107). Cooling medium is fed in at (108), (109), (110), (111) and fedout at (112), (113), (114), (115). At (116) a mixture of liquid andcrystals is withdrawn from a compartment to the slurry thickener (notshown) belonging to that compartment, while at (117) a mixture is tointroduced in that compartment, consisting of liquid from thatcompartment, liquid from the preceding compartments and crystals fromthe succeeding compartment, this mixture coming from the upper part ofthe next thickener (not shown).

FIG. 3 is a cross section along the line III--III in FIG. 2. At (201) isshown the cylindrical crystallization vessel, at (202) and (203) wallsof the cooling tray, at (204) the hollow axle. Cooling medium is fed inat (205) and fed out at (206). The flow pattern of the cooling medium isdenoted with (207).

FIG. 4 is a cross section of part of a cooling tray along the lineIV--IV in FIG. 3. The metal walls are indicated with (301). The coolingmedium is fed out (or fed in) at (302). The narrow slit (304) ensures aneven distribution of the cooling medium.

An apparatus as shown in FIG. 1 may have in the case of a freezeconcentration process a capacity of about 50 kg water removal per hour.The cooling trays (12) may have an outside diameter of about 525 mm andan inside diameter of about 224 mm. The thickness of these trays may beabout 20 mm.

The crystallization compartments (8), (9), (10) may have a height ofabout 375 mm, and the compartments (7) and (11) may have a height of 250mm. The total height of the crystallization vessel may be about 2 m.

The common axle (22) of the thickeners (19), (29), (34), (37), (38) mayhave a diameter of about 90 mm and the inner diameter of the cylindricalenclosure means (as denoted 401 in FIG. 5) may be about 120 mm. Thisresults in an annular space of about 15 mm. The height between thefilter means and the under flange may be about 50 mm, the height of thefilter means about 40 mm, and the height of the stationary vanes about20 mm, while the tilted vanes may have a height of 10 mm. The totalheight of one thickener may be about 160 mm, the flanges not included.The height of the stationary vanes above the filter means in thickener(38) may be about 150 mm. The total height of the stack of thickeners,inclusive flanges, may be about 1.20 m.

In FIG. 4A a preferred embodiment of the invention is shown partly cutopen lengthwise. The following remarks refer to the first and secondcompartment. At (601) we see the first compartment which is fed with thesolution to be freeze concentrated, in the same way as in FIG. 1 (feedin not shown here), and at (602) we see the second compartment. Coolingtrays, as already described are indicated with (603) and (604);scrapers, as already described in FIG. 1 are shown at (605) and (606).Moreover the compartments are provided with stirring means, one of whichis indicated with (607). These stirring means consist of rods, attachedto the main axle (608), provided with vanes.

The slurry thickeners (609) and (610) are directly attached to the mainbody of the apparatus. The wash column for the separation of the icecrystals from the first compartment (601) is shown at (611). The slurrythickeners and the wash column are separately actuated by the motors(612), (613) and (614). They will be described in more detail furtheron.

A slurry of ice crystals and liquid is pumped by the pump (615) to thewash column (611), functioning in essentially the same manner as alreadydescribed for the embodiment shown in FIG. 1. The liquid, leaving thewash column at (616) reenters the compartment (601) at (617). Part ofthe liquid passes on to the second compartment through the pressurevalve (618). The slurry of compartment (602) is fed to the slurrythickener (609) by the pump (619) and the liquid is recirculated to thesame compartment (602) as already described for the compartment (601).Again part of the recirculated liquid is passed on to the nextcompartment to which purpose the pressure valve (620) serves.

In FIG. 5 a slurry thickener is shown (see (19) in FIG. 1), cut openlengthwise. (At (401) we see the cylindrical enclosure means, at (402) aside view of the axle, at (403) and (404) tilted vanes, attached to theaxle and having the function to push the crystal mass upward. At (405)there are likewise shown tilted vanes having the function to cut, breakup and forward the crystal mass. The axle (402) is actuated by the motor(406). At (407) and (408) are shown stationary vanes attached to theinside of the cylinder (401). Pens (409) attached to the axle help inkeeping the crystals in suspension. At (415) pens attached to the insideof the cylinder (401) are shown. (At (410) is shown the feed in for theliquid from the preceding crystallizing compartment and at (411) thefeed out of the mixture of liquid from the preceding crystallizingcompartment, the same crystallizing compartment, and crystals from thesucceeding compartment. At (412) we see the feed in for the mixture ofcrystals and liquid, at (413) the filter retaining the crystals and at(414) the feed out for the liquid drained from the crystals between thefilter (413) and the axle (402).

FIG. 6 is a cross section according the line VI--VI in FIG. 5. Again thecylindrical hull is shown at (401), the hollow axle at (402), tiltedvanes at (404), stationary vanes at (407), the filter at (413), the feedin for crystals and liquid at (412), the feed out for the drained outliquid at (414). At (416) we see the flange with holes (417) to fix thehull to the bottom of the slurry thickener.

In the FIGS. 6A, 6B and 6C a preferred embodiment of the slurrythickener is shown. In FIG. 6A the slurry thickener is cut openlengthwise, in the same way as in FIG. 5.

The axle (702) consists of an inner core (which will be shown in FIG.6B), surrounded by rings one on top of the other. For reasons of claritythe dividing lines between the rings are only shown for the ring (701)which will be described below.

The differences with FIG. 5 are to be seen in the upper part of thefigure. At (701) we see a ring attached to an axle which will be shownin FIG. 6B as (702), and a disk (701') forming part with that ring,provided with slanted slots (703). This disk (701') fits snugly in thehull (718) of the slurry thickener. The number of slots may vary, e.g.from 1 to 4 and is dependent on the quantity of ice which has to behandled per time unit. Each slot is at the side of the filter providedwith a knife (704). At the other side the slots are closed by springytin metallic strips (705). When the axle (702) with the disk (701) isrotated (seen from above clockwise) the mass of ice crystals, compactedin the annular space (706) is desintegrated. The metallic strips (705)are lifted when the pressure exceeds a predetermined value and thedesintegrated mass passes through the slots (703).

The ice crystals are now further forwarded in the annular space (707),provided with stationary vanes (708). At (709) are shown tilted vanes(as also already described with their function in FIG. 5). In theannular space (707) transport will cause a certain renewed compactionand the mass will be loosened by the tilted vanes (709). The loosenedcrystal mass passes now in the `mixing compartment` (710) provided withstationary pins (711) and pins (712) attached to the rotating axle(702). The vanes (713), tangentially mounted to the axle (702) help inforwarding the ice crystals, now mixed with liquid entering at (714),into the outlet (715).

The stationary vanes (708) have the following function. They serve toavoid that the desintegrated mass of ice passing through the slots (703)rotate along with the disc (701'). The ice would accumulate above thatdisc (701') and prevent the metallic strip (705) from opening. The vanes(708) thus to say sweep the disc (701') and the ice will be transportedin axial direction. The vanes (708) will preferably be relatively longto prevent liquid entering at (714) to enter the annular space (706) byleakage between the disc (701') and the hull (718).

Now coming back to FIG. 4A it can be said that the slurry thickeners(609) and (610) have the construction of the thickener just describedand shown in FIG. 6A, with the exception that the upper part (the mixingcompartment), which goes to say the part above the line A A' issuperfluous. The part below that line is directly attached to thecompartments (601) and (602) by flanges.

FIG. 6B shows a top view of a cross section taken along the lineVIB--VIB, in FIG. 6A while FIG. 6C shows the ring denoted with (701) inFIG. 6A in side view and more in detail. At (702) we see the axle aroundwhich rings are disposed one on top of the other. The rings rotate alongwith the axle (702) by the key (716). The ring (701) carries the disc(701') as already said. One slot is to be seen at (703), one knife at(704), the springy metallic strip at (705), this last being attached tothe disc (701') by a bolted block (717).

In FIG. 7 the construction is clarified for an embodiment of theinvention whereby the filter means consist of radially oriented pairs offilter surfaces, bridging the annular space between the cylindrical hulland the axle. Here again a cross section is shown perpendicular to thelong axis of a thickener-washer.

At (501) we see the cylindrical hull, at (502) the hollow axle, at (503)the pairs of filter surfaces, held apart by the corrugated gauze (504).A cylindrical wall (505), with slits (506) creates a narrow annularspace (507), communicating with the spaces between the pairs of filtersurfaces (503) and with the feed out (507) for the drained out liquid.At (508) we see the tilted vanes attached to the hollow axle (502).

In FIG. 8 the wash column (611) of FIG. 4A is shown in more detail.

The slurry enters at (801). Pins, rotating with the axle are shown at(802); stationary vanes at (803). The filter is denoted with (804). Theliquid, passing through the filter leaves at (805). Tilted vanes areshown at (806). At (807) small stationary vanes are shown.

The annular space (808) is appreciably longer than in the slurrythickener as described in FIG. 6A.

The cutting device which will presently be described in FIGS. 8A and 8Bmore in detail is to be seen at (809). Somewhere between the smallstationary vanes (807) and the cutting device (809) a wash front has tobe formed between washwater and the liquid which has to be washed outbetween the ice crystals.

The reason that the annular space (808) is relatively long is to befound in the necessity to allow for some tolerance for the position ofthe wash front.

The ice passes through the slots (810) into the annular space (811), andis slushed away at (812) through the melter (813). The pump (814) willrecirculate most of the water back to (815), for the slushing away ofthe ice as just described. A quantity of water corresponding to the icefed in at (801) will be removed through the valve (816), governed by thecontrol unit (817), which is fed by the converter (818). The convertergets signals from the temperature sensing devices (819) e.g.thermocouples. As well known the temperature at which thecrystallization occurs, is a measure of the concentration of dissolvedsolids in the remaining liquid.

FIG. 8A is a top view of a cross section along the line VIIIA--VIIIA inFIG. 8. FIG. 8B shows a detail of FIG. 8A in side view. The cuttingdevice, which in FIG. 8 was denoted with (809) is composed of a ring(821), which rotates with the axle (820) by the key (820'). This ring(821) carries blocks (822), provided with knives (823), which in theirturn are provided with a cutting "beak" (824). Between the blocks andcutting knives we see in FIG. 8A the slots (810).

We claim:
 1. Apparatus for the continuous freeze concentration ofaqueous solutions comprising in combination:(a) enclosure means defininga cylindrical crystallization zone; (b) a rotatable axle coaxial withthe crystallization zone mentioned under (a); (c) a plurality of coolingtrays within the crystallization zone mentioned under (a), distributedat preselected distances along the axle mentioned under (b), andsubstantially perpendicular to that axle, said cooling trays extendingin radial direction from the inner wall of the enclosure means mentionedunder (a) to the axle, such as to divide the crystallization zone,mentioned under (a) in a number of cooling compartments; (d) wipermeans, adapted to cooperate with and wipe the surface of the coolingtrays, mentioned under (c); (e) means to separate the ice crystals ofeach of the cooling compartments, mentioned under (c) from liquid inthat compartment; (f) means belonging to each cooling compartment toseparate the ice crystals of the second and additional coolingcompartments from liquid and pass said ice crystals to the procedingcompartment; (g) means to pass liquid obtained from the second to thepenultimum separating means mentioned under (f) to the succeedingcooling compartment; (h) means to separate the ice crystals of the firstcooling compartment from liquid and feed out said ice crystals; (i)means to pass liquid obtained from the first separating means mentionedunder (h) to the second cooling compartment; (j) means to feed in theaqueous solution in the first cooling compartment; (k) means to recoverliquid obtained from the last separating means as a product.